1. Field of the Invention
The subject matter of this invention is related to circuit interrupters generally and more specifically to those kinds of circuit interrupters in which an interlock is provided to prevent the handle mechanism from showing that the circuit breaker is open when in fact the contacts thereof are welded closed. It is also related to circuit breakers that evolve arc quenching gas which under pressure may affect other parts of the system and lastly it is related to a multi-rate spring utilized for the magnetic trip device.
2. Description of the Prior Art
Molded case circuit breakers are well known in the arc as exemplified by U.S. Pat. No. 4,503,408 issued Mar. 5, 1985 to Mrenna et al, entitled "Molded Case Circuit Apparatus Having Trip Bar With Flexible Armature Interconnection" and assigned to the assignee of the present application. The foregoing is incorporated herein by reference.
In circuit breakers of the kind mentioned above is necessary to give an indication to an operator that the contacts thereof have not opened when the operator had been led to believe that they have. The method for doing this in the prior art is to introduce over-ride means which prevent the handle of the circuit interrupter from indicating an open condition if such has is not occurred. In order to do that, intricate mechanisms are provided in the operating mechanism between the closed contacts and the handle mechanism to prevent an indication that the circuit breaker has been opened. It would be advantageous if a welded contact interlock could be provided for the present circuit breaker apparatus which was relatively inexpensive, reliable and simple to operate.
Molded case circuit breakers often require the contacts thereof to be moveable to the opened disposition in either one of two ways. The first and normal way is to have a molded crossbar in which the base of the moveable contact arm is secured to pivot the moveable contact arm and thus its contact away from the fixed contact either my manual operation or by an electrical trip operation. However, it is also desirable to quickly separate the contacts without relying upon a relatively slow electrical trip operation upon the occurrence of the severe overload current. To do this the base of the fixed contact arm is spring loaded by way of a cam rider system within the aforementioned crossbar so that it may be pivoted therein without movement of the crossbar and held in the open position until the electrical trip mechanism causes the crossbar to open. Such a system is taught in U.S. Pat. No. 5,565,827 issued Oct. 15, 1996 to Gula et al and entitled "Circuit Breaker With Current Conducting Blow-Open Latch" and assigned to the assignee in the present application and which is incorporated by reference herein. As circuit breaker contacts open, an electrical arc is drawn which in many circuit breaker operations interacts with material within the circuit breaker arc chamber to produce a gas which is useful for cooling the arc in some instances and also to assist in pushing the arc out into an arc chamber where it is broken up, dissipated and interrupted. Unfortunately, in some instances much of the gas is hot enough to be a problem for other mechanical parts of the circuit breaker. One of the problems which is most closely associated with the hot gas by reason of proximity is its effect on the spring mechanism of the aforementioned blow open latch arrangement. It would be desirable to provide a cam rider system for the latch which would also seal off the spring mechanism from the hot gases.
The action to automatically open an electrical circuit breaker often requires a magnetic tripping device which utilizes a magnetic coil. When a current of proper magnitude such as a fault current flows through the coil, the increased magnetic force draws the moving core downwards towards the stationary core. A plunger that is fixed to that moving core contacts a trip bar and rotates the trip bar to unlatch the circuit breaker mechanism thus causing the aforementioned crossbar to rotate to thus cause the movable arm to move the moveable contact away from the fixed contact and thus eventually interrupt the electrical current. The force necessary to provide this function is adjustable by the utilization of the spring. The spring surrounds the aforementioned moving core and is held in fixed position at one end while a flanged end of the moving core compresses against the other end. The force necessary to compress this spring is constant through all instantaneous trip ranges. This is appropriate for ranges which require a relatively small adjustment span of say an instantaneous trip levels of five to ten times the continuous current rating. However it is desirable in some instances to make the adjustable trip range larger, for example between three and eleven times the continuous current rating. This would call for a higher range spring. Such a spring would be perhaps very accurate at either the higher or lower range of tripping because of the mechanical force it produces against the moving core but it would be less forceful at the opposite end of the trip range. Consequently it would be desirable if a spring arrangement could be found which was accurate and equally forceful at both ends of an expanded trip range.